1. Field of the Invention
The present invention relates to a high-density laminate-type semiconductor apparatus having a plurality of semiconductor devices mounted on a plurality of flexible substrates. In particular, the present invention relates to a laminate-type semiconductor apparatus using a plurality of foldable flexible substrates. The present invention is utilizable as an assembly structure of a variety of semiconductor apparatuses such as a MOSFET, MISFET and other field-effect transistors, for example, and yet, the present invention can also be utilized as a practical technique for fabricating a laminate-type semiconductor apparatus by way of using a plurality of foldable flexible substrates.
2. Description of the Related Art
Because of the demand for further downsizing and higher density, higher density mounting of component parts has thus been demanded for electronic apparatuses using semiconductor apparatuses. To achieve this, in semiconductor apparatuses being a constituent of the electronic component parts, there are such proposals with regard to so-called xe2x80x9cchip-size-package (CSP)xe2x80x9d or xe2x80x9cmulti-chip-module (MCM)xe2x80x9d each having such a size substantially equivalent to that of a semiconductor apparatus, or such a laminate-type semiconductor package comprising plural elements laminated in the height direction for contraction of the mounting area, for example. The above-cited packages have already been provided for practical services.
There are various proposals with regard to the laminate-type semiconductor apparatus using a foldable flexible substrate having various semiconductor devices mounted thereon, which is laminated on predetermined areas of the folded substrate, and yet, this apparatus has actually been provided for practical use. It should be noted that the terms xe2x80x9cfoldablexe2x80x9d mentioned in the present specification implies that the above-cited laminate-type semiconductor devices can be processed via lamination by allowing desired areas to be superposed with each other. In this case, clear fold is not always required, but insofar as lamination can be effected, and yet, insofar as flexibility is retained, even such a substrate with curved form, plate-form, tape-form or sheet-form may also be used. With regard to the laminate-type semiconductor-device mounted apparatus, refer to the Japanese Patent Application Laid-Open Publication No. HEISEI-11-135715/1999, for example.
There is such a proposal on a conventional laminate-type semiconductor apparatus or a semiconductor package as the one shown in FIG. 3 via a lateral sectional view.
According to the above-cited conventional laminate-type semiconductor apparatus, a plurality (four, in this case) of semiconductor elements comprising a first device 3, a second device 4, a third device 4, and a fourth device 30, are laminated in the vertical direction of FIG. 3. As shown in FIG. 4 via a development view, the first device 3, the second device 4, the third device 5, and the fourth device 30, are mounted on edge portions of crossed members of a cross-form flexible substrates before being folded into an assembly, whereby forming a laminated structure by way of superposing four devices one after another like the one shown in FIG. 3. The development view shown in FIG. 4 is illustrative of a position at which back surface shown in FIG. 3 corresponding to an externally-connected terminal disposing area 6 is visible on the upper side.
Detail of the development view shown in FIG. 4 will be described below. Initially, by way of utilizing a plurality of substrates made of polyimide resin, a plurality of flexible substrates foldable as a whole are assembled as shown in FIG. 4 via the development view. In this conventional example, the flexible substrates are assembled into a crossed formation. The center portion of the crossed substrates is determined as the externally-connected terminal disposing area 6 for accommodating an externally connected terminal 7 as shown in FIG. 3. Next, originating from the center portion, four of the semiconductor-device mounting areas 61, 62, 63, and 64, are independently formed via foldable wiring distributing areas 11, 12, 13, and 50, respectively, to complete formation of a wiring substrate 2. Individual semiconductor devices are mounted on respective semiconductor-device mounting areas 61, 62, 63, and 64 formed on the wiring substrate 2. More particularly, the above-referred semiconductor devices comprising the first device 3, the second device 4, the third device 5, and the fourth device 30, are mounted on the corresponding semiconductor-device mounting areas 61, 62, 63, and 64. This completes such a semiconductor apparatus having a plurality of semiconductor devices 3, 4, 5, and 30 mounted on the back-surface side (inside of the apparatus) of the externally-connected terminal disposing area 6.
Reference codes xe2x80x9caxe2x80x9d, xe2x80x9cbxe2x80x9d, xe2x80x9ccxe2x80x9d, and xe2x80x9cdxe2x80x9d shown in FIG. 4 respectively designate connecting parts between respective semiconductor-device mounting areas 61, 62, 63 and 64 and wiring extended areas 11, 12, 13 and 50.
In terms of such a semiconductor package comprising a laminated assembly of semiconductor devices laminated on a polyimide substrate, introduction of module structure has recently been promoted in the assembly of memory devices and also in the assembly of logic devices and memory devices. Because of this, the number of laminated layers tends to become greater. However, as the number of laminated layers increases, thermal radiation generated by individual elements becomes a critical problem. In the above-cited conventional laminate-type package, the laminate-type structure has the substrate 2 which is developed as shown in FIG. 4. On the other hand, as shown in FIG. 3, when forming a laminate-type package by serially laminating the first device 3, the second device 4, the third device 5, and the fourth device 30, individual lamination causes thermal radiation to grow to necessitate any counter-measure to deal with this problem.
Further, whenever laminating semiconductor devices on a flexible substrate, a problem may be generated by effect of folding stress via a folding process. For example, when forming a laminate-type package by way of folding a flexible polyimide substrate, because of the folding stress via the folding process, leveling effect can hardly be achieved throughout the above-referred externally-connected terminal disposing area 6, thus raising such a problem. Because of this, in order to improve effect of connection between the externally-connected terminal disposing area 6 and the substrate for accommodating it via a soldering process, it has thus been necessary to implement any measure to ensure leveling effect, in other words, improve the parallelism.
As was described above, in the conventional laminate-type semiconductor apparatuses, in order to achieve higher density of such a package mounted with laminated semiconductor devices, a laminate-type structure is formed by way of folding a flexible substrate which is made of a flexible polyimide plate or a polyimide tape, for example. However, when a number of semiconductor devices are laminated, it is quite difficult to suppress amount of heat generated by respective semiconductor devices to damage operating function of the package itself. On the other hand, in the case of lamination of semiconductor devices on a flexible polyimide substrate such as a flexible polyimide plate or a polyimide tape, for example, via a folding process, it had thus been necessary to implement any measure to level off the substrate before mounting semiconductor devices on the substrate via a soldering process, and yet, it had thus been necessary to fully ensure strength of the connected effect between them.
The object of the present invention is to fully solve the above-referred technical problems by way of providing a novel semiconductor apparatus which is free from incurring malfunction caused by thermal radiation even in the case of laminating a plurality of semiconductor devices on a flexible substrate, and yet, provided with a fully leveled substrate with sufficient strength whereby enabling the semiconductor devices to be mounted thereon in a high density.
In the semiconductor apparatus according to the present invention, initially, a flexible substrate is folded (it is also possible to utilize such a flexible substrate made of an opaque polyimide plate). Next, a plurality of semiconductor devices (four devices, for example) are serially laminated on the flexible substrate. Next, in order to fully level off an externally-connected terminal disposing area, a reinforcing plate is set on the part of the externally-connected terminal disposing area via a material portion having stress-relaxing function by means of adhesion with a gelled adhesive agent, for example. Next, a radiating plate is disposed on the surface of a side opposite from the externally-connected terminal disposing area of the above-referred flexible substrate.
Concretely, in the semiconductor apparatus based on the above structure, a radiating plate such as a copper plate, for example, is adhered onto the uppermost portion of the mounted semiconductor devices by means of adhesion with an adhesive agent. Further, in order to fully level off the externally-connected terminal disposing area, a reinforcing plate which is made of a ceramics plate is secured with an adhesive agent capable of relaxing stress.
By virtue of the above arrangement, it is possible to realize a high-density laminate type package which is free from being subject to restriction from thermal radiation characteristic and restriction on the bonding with a mother board for mounting semiconductor devices without damaging overall function of the package itself.
According to the present invention, it is possible to realize such a high-density laminate type package without being subject to restriction from thermal radiation characteristic, and yet, without damaging proper function of semiconductor devices.
The present invention specifies utilization of a folded structure of a flexible substrate. It should be understood, however, that, even if the flexible substrate is not manufactured by way of actually being folded, it is allowable for use insofar as it is complete with a folded structure in consequence. In the case of manufacturing the flexible substrate of the present invention via a folding process, even when the flexible substrate is not folded after fully mounting semiconductor devices thereon, it is still allowable for use insofar as semiconductor devices are mounted on the substrate with a folded form in consequence.
The Japanese Patent Application Laid-Open Publication No. HEISEI-6-168985/1994 discloses a structure for laminating reinforcing members in the art of using highly flexible film material in regard to a structure for mounting semiconductor devices. It should be understood however that the semiconductor apparatus specified in the above-identified Publication is not of a laminate type, and the technique disclosed therein is totally independent of the present invention.